A legislator in the Russian city of St Petersburg has said he will seek to annul a marriage between two women, one of whom is transsexual.
Vitaly Milonov, an opponent of gay rights, said the wedding on Saturday was an "insult" to Russian families.
Gay marriage is banned in Russia, but the couple were not denied a ceremony because according to their passports one is a man, the other a woman.
It is unclear whether this was Russia's first case of such a union.
A controversial 2013 law on "anti-gay propaganda", makes it illegal to distribute information about homosexuality to children in Russia.
Correspondents say the law comes as part of a campaign for "traditional values", with members of the lesbian, gay, bisexual and transgender (LGBT) community feeling increasingly threatened.
'Insult to millions'
The couple, named as Irina Shumilova and Alyona Fursova, arrived at a register office in St Petersburg, both wearing white bridal dresses and carrying bouquets.
They posted pictures of the ceremony on the Russian social media site Vkontakte.
Irina, who describes herself as transsexual rather than transgender, is still undergoing hormone therapy.
Mr Milonov - one of the most ardent supporters of the 2013 law - told Russian media the staff at the registry office should be tried for treason or criminal negligence.
He would seek the marriage's annulment to avoid "an ugly insult to millions of Russian families in the future", he added.
"There are certain moral standards which it is vital to implement," he said. "These mad people should be banned altogether from getting married."